1. Field of the Invention
The present invention pertains to a piezoelectric-type transducer particularly adapted to generating or receiving acoustic signals and having a hydraulic fluid coupling for amplifying mechanical displacement of the piezoelectric actuator.
2. Background
Piezoelectric elements are widely used as conversion devices for electrical to mechanical energy and vice versa. One application for piezoelectric signal transmitting elements is in conjunction with so-called acoustic-type well logging tools wherein acoustic signals are generated in a fluid filled borehole and propagated through the earth formation surrounding the borehole and whereupon reflected acoustic signals are received by suitable transducer elements for determining certain formation characteristics. Piezoelectric elements are particularly attractive for use in such applications because of their mechanical simplicity and reliability, frequency response and energy conversion efficiency.
One disadvantage of piezoelectric structures in transducer applications is that they have a relatively small elongation or strain characteristic which does not always effectively couple energy to and from the piezoelectric structure. Accordingly, relatively complex piezoelectric structures have been utilized, particularly in acoustic energy transducer elements such as those described in U.S. Pat. No. 4,649,525 to F. A. Angona et al, and U.S. Pat. No. 4,715,019 to Medlin et al.
Since piezoelectric actuators are particularly useful for generating acoustic waves in fluids for various applications, there has been a long-felt need to provide an acoustic signal transmitter and/or receiver adapted for the dimensional constraints and operating environments associated with such applications as underwater marine signalling and for use in conjunction with wellbore tools. These applications demand a high mechanical advantage in the transducer in order to suitably generate and receive pulse-type acoustic signals. The mechanical advantage provides a means to transform the large force and small displacement of the piezoelectric element into a smaller force and larger displacement in the fluid that is acted upon. Such a transformation is important because of the large acoustic impedance contrast between the fluid and the piezoelectric element. One improvement in such types of transducers is described in U.S. patent application Ser. No. 07/319,067 filed Mar. 6, 1989 to Keith W. Katahara and assigned to the assignee of the present invention. The present invention is directed to another improved piezoelectric-type transducer which includes a novel displacement amplifier for the piezoelectric actuator.